code: def test_delete_file(self):
      with fh.FTPHook() as ftp_hook:
          ftp_hook.delete_file(self.path)
  
      self.conn_mock.delete.assert_called_once_with(self.path)
  
imports: from __future__ import annotations
  from io import StringIO
  from unittest import mock
  import pytest
  from airflow.providers.ftp.hooks import ftp
label_desc: Use image node_id 8 for calling the TestFTPHook obj's underlying member method code with example usage: obj.test_delete_file() without return types